The present disclosure is directed generally towards thin film composite barrier coatings having improved resistance to diffusion of chemical species and to devices incorporating such composite thin film coatings. In particular, the present disclosure relates to electronic devices, such as organic light emitting diodes (“OLEDs”), that incorporate such composite thin film coatings and have improved stability in the environment.
As is well known in the art, electronic devices, and display technologies such as OLEDs, require ultra high barrier protection against oxygen, moisture and other gases. Conventional electronic devices are built on glass or metal substrates because of the low permeability of glass or metal to oxygen and water vapor. High permeability of these and other reactive species can lead to corrosion or other degradation of the devices. However, glass and metal substrates are not suitable for certain applications in which flexibility is desired. In addition, manufacturing processes involving large glass and metal substrates are inherently slow and, therefore, result in high manufacturing cost.
Flexible plastic substrates have been used to build electronic devices. However, these substrates are not impervious to oxygen and water vapor, and, thus, are not suitable per se for the manufacture of long-lasting electronic devices. In order to improve the resistance of these substrates to oxygen and water vapor, alternating layers of polymeric and ceramic materials have been applied to a surface of a substrate. It has been suggested that in such multilayer barriers, a polymeric layer acts to mask any defects in an adjacent ceramic layer to reduce the permeation rates of oxygen and/or water-vapor through the channels made possible by the defects in the ceramic layer. However, an interface between a polymeric layer and a ceramic layer is generally weak due to the incompatibility of the adjacent materials, and the layers, thus, are prone to be delaminated.
Graded-composition barrier coatings disposed on the surfaces of electronic devices and substrates such as those disclosed in U.S. Pat. No. 7,015,640, have been used to reduce permeation rates of chemical species therethrough. These barrier coatings comprise a material the composition of which varies substantially continuously across a thickness thereof. The graded composition barrier coating provides reduced permeation rates for water vapor and oxygen as well as other chemical species and may be suitable for many applications, such as devices in which flexibility is desired. During deposition, varying the relative supply rates or changing the identities of reacting species results in a coating that has a graded composition of reaction or recombination products of the reacting species across its thickness. The graded composition barrier coating does not have distinct interfaces at which the composition changes abruptly, rather it has a substantially continuous transition of materials.
However, many organic electronic devices, both rigid and flexible, have severe surface topology where surface features can significantly exceed the thickness of the thin film barrier coating deposited using a method known in the art. For example, passive matrix displays may possess geometry, or severe surface features, usually microns high, that make it difficult for the barrier coating to completely and hermetically cover the surface features over large areas. This geometry may create a “shadow zone.” Furthermore, the presence of contamination particles on any desired coating surface may create a shadow zone or prevent deposition of an effective diffusion barrier coating through traditional prior art methods or a baseline method that is optimized for a substantially planar device.
As a result, there is a continued need for robust films that have reduced permeation rates of environmentally reactive materials. It is also desirable to provide such films to produce flexible electronic devices that are robust against degradation due to environmental elements.
This problem has previously been addressed in a combination of separate processes. In a method known in the art, a substantially thick smoothing or planarizing layer is deposited on the device, using a wet coating technique such as spincoating, dipcoating, spraycoating, etc. Subsequently, a separate barrier coating deposition process, such as plasma enhanced chemical vapor deposition (PECVD), is used to deposit a barrier coating on the device. The combination of the primary barrier coating process with a second wet or dry coating process is expensive, decreases product throughput and increases process tact time.
Therefore, there is a need for a novel barrier coating configuration that enables the continuous and effective coverage over such severe surface topology, in a single barrier deposition process, thereby protecting the device from degradation due to the ingress of harmful permeants while simultaneously providing a commercially advantageous, low tact time encapsulation process. Such a barrier coating will substantially conform to a profile of the device. “Substantially conforming,” “substantially conformal,” or “substantially conforms” are terms that will be used interchangeably hereinafter and mean that a thickness of a property is approximately equivalent about the area or along the surface being described as possessing this property.
Accordingly, an embodiment of the present disclosure includes an improvement of a baseline method of depositing a coating on a device having a first portion and a second portion, where the second portion is in a shadow zone and where the coating is deposited using a first predetermined set of process parameters having a first ratio of a thickness of the coating on the second portion to a thickness of the coating on the first portion. In the improved method of an embodiment of the disclosure, the coating is deposited on the device using a second set of predetermined process parameters such that the coating substantially conforms to a profile of the device and a second ratio of a thickness of the coating on the second portion to a thickness of the coating on the first portion is greater than the first ratio using the baseline method.
An additional embodiment includes an improvement of a baseline method of depositing a barrier coating on a device having a first portion and a second portion, where a surface of the second portion is in a shadow zone and where the barrier coating comprises a substantially continuous transition from a substantially inorganic zone deposited at a first thickness to a substantially organic zone deposited at a second thickness and a buffer layer deposited using a reactive ion etching PECVD deposition mode (“RIE mode”), resulting in a first water ingress rate. “RIE mode,” as used herein, refers to a PECVD deposition configuration where a substrate, for example, is placed on the powered electrode. A plasma enhanced mode (“PE mode”), as used herein, refers to a configuration where a substrate, for example, is placed on the ground electrode. The improvement of the baseline method includes depositing the substantially inorganic zone at a third thickness and depositing the substantially organic zone at a fourth thickness wherein the third thickness is greater than the first thickness and the fourth thickness is greater than the second thickness, and depositing the buffer layer in PE mode, resulting in a second water ingress rate wherein the second water ingress rate is less than the first water ingress rate.
Another embodiment of the present subject matter describes a method for depositing a barrier coating where the method provides a device having a surface with a first surface portion and a second surface portion where a surface of the second surface portion is in a shadow zone, where the device is pretreated such that the deposition rate of a barrier coating on the first surface portion is altered and where the shadow zone is substantially unexposed to the pretreating, and where the barrier coating is deposited on the first and second surface portions, substantially conforming to a profile of the device.
A further embodiment includes a method for depositing a barrier coating where an apparatus is provided having a substrate and an electronic device, where a surface of the electronic device is in a shadow zone, where the apparatus is pretreated such that a deposition rate is altered on a surface exposed to the pretreating and where the shadow zone is substantially unexposed to the pretreating, and where a graded-composition barrier coating, having an organic and inorganic material composition that varies substantially continuously across a thickness thereof, is deposited using plasma enhanced chemical vapor deposition such that the barrier coating substantially conforms to a profile of the apparatus.
Yet another embodiment of the present subject matter provides an apparatus having a substrate, an electronic device attached to the substrate where a surface of the electronic device is in a shadow zone and the surface has a deposition rate of a barrier coating different than a deposition rate of the barrier coating on a surface outside of the shadow zone, and a graded-composition barrier coating substantially conforming to a profile of the apparatus where the coating comprises an organic and an inorganic material, the composition of which varies substantially continuously across a thickness thereof.
These embodiments and many other objects and advantages thereof will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the embodiments.